Digital cameras have increased tremendously in popularity over the last decade, as high quality image sensor cameras have become affordable. Miniaturization of both optics and electronics have resulted in extremely compact camera modules, and it has therefore become a common approach to introduce digital cameras in mobile phones. Initially, still image cameras were employed, but also video recording cameras are commonly included in state of the art mobile phones. A mobile phone with a built in digital camera is often referred to as a camera phone.
For the purpose of capturing high quality images, i.e. still pictures or video, the mobile phone is often equipped with a primary built in camera with an image sensor of several mega pixels. When operating the primary camera, the display is typically used as a viewfinder, by presenting the images presently captured by the primary camera. The primary camera is therefore normally aimed in the opposite direction of the display. Upon pushing a button or similar, a snapshot may be taken, or a video recording may be initiated. Captured images may be stored in a memory of the phone, and shared with other users, e.g. by presenting them on a display or by sending an mms.
Since the introduction of the so called 3rd generation (3G) type of mobile telephony systems, such as WCDMA, mobile video conferencing services have also been developed. In a typical mobile video conferencing scenario, a user captures a video signal of his or her own face with a built in camera, and sends the video signal to a remote party, while a video signal received from the remote party is presented on a display of the phone. Normally, a small image of the signal captured of the user's own face is simultaneously presented in a smaller frame of the display, so as to guarantee that the camera is properly aimed. A separate video conference camera, or secondary camera, is therefore typically included. The secondary camera is aimed in a direction substantially common with a normal viewing direction of the display, and therefore also in a substantially opposite direction compared to the primary camera. Video conferencing systems are often defined to make use of a fairly low resolution, such as VGA or QCIF, in order to minimize the required communication bandwidth, and the video conference camera may therefore be fairly simple.
Digital images captured by a primary camera of a mobile phone are presented on the display of the phone, or on a connected external computer screen. The user is often free to compose images in any way, including changing the orientation of the camera. Horizontal or “landscape” orientation is displayed correctly on the display. However, when using a vertical or “portrait” orientation, the image is still saved to file in the orientation used, which means that it will be displayed as rotated by 90 degrees. In many mobile phones the user has an option to use a software application to rotate the image in the correct direction. However, this is a manual operation and can be quite time-consuming if many images have been captured. If it is not done, viewing a slideshow of the images means that you have to rotate the phone when ever the orientation of the images change. If you are viewing the images on a computer screen or a TV, this operation becomes almost unthinkable.
The problem of image orientation in digital cameras is not confined to the art of mobile phones, but to digital cameras as such, and different solutions for more or less automatic image orientation adjustment in digital cameras as such have been suggested.
U.S. Pat. No. 5,900,909 to Parulski et al. discloses an electronic still camera provided with an electronic image sensor for generating an image signal corresponding to a still image of a subject and an orientation determination section for sensing the orientation of the camera relative to the subject. The orientation determination section provides an orientation signal recognizing either the vertical or the horizontal orientation of the camera relative to the subject. An image processor is responsive to the orientation signal for processing the image signal and correcting the orientation thereof so that the still image is output from the image processor in a predetermined orientation. In this way, the electronic still camera can be positioned in a variety of orientations relative to a subject, including both clockwise and counterclockwise vertical “portrait” orientations and a horizontal “landscape” orientation, without affecting the orientation of the images output by the camera. In order to determine the orientation of the camera, an orientation sensor is included in the camera, in the form of mercury-filled switches or photo-interrupter type switches.
US 2004/0017506 A1 to Livingston discloses a similar approach, in which a camera includes a camera orientation sensing system configured to determine the orientation of the camera, the sensing system including an orientation sensor that is fixedly positioned relative to the camera body in an angled orientation such that the longitudinal axis of the sensor is not parallel to either of the horizontal or vertical axes of the camera body. Each orientation sensor typically includes a gravity-sensitive switch, such as a mercury-filled switch.
However, any inclusion of physical auxiliary means for orientation detection, such as switches, also involves increased cost and requires some space within the camera device in question.